The invention relates to a tape-type superconductor, comprising                an elongated substrate, in particular a metal tape, and        a continuous superconducting layer, in particular of a HTS type material, deposited on the substrate.        
Such a superconductor is known from A. Usoskin et al., IEEE Trans. On App. Supercond. 17 (2), pages 3235-3238 (2007).
Superconductors may transport electric currents without ohmic losses. However, in practice, superconductors may experience other types of losses. These losses heat up the superconductor, what may cause the superconductor to become normally conductive when the critical temperature Tc is reached. Even when the superconductor stays superconductive, losses increase the cooling costs (e.g. the consumption of liquid helium or liquid nitrogen) for keeping the superconductor below Tc. Therefore, in general, superconductors with low losses are preferred.
Losses in superconductors may be caused, in particular, by hysteretic effects. When a superconductor experiences a magnetic field, the superconductor squeezes out magnetic flux lines (“perfect diamagnetism”), wherein current loops are induced in the superconductor, generating an opposing magnetic field. When the magnetic field changes, the current loops vanish again and dissipate their energy, what heats up the superconductor, and other current loops are induced.
Superconductors may experience alternating (changing) magnetic fields for a number of reasons, for example the superconductor may be operated near a rotating magnet (e.g. in a motor), or the superconductor carries an alternating current (ac current) what causes an alternating self field in the vicinity of the superconductor.
In order to reduce losses in superconductors due to alternating magnetic fields (“ac losses”), it has been proposed to break up a superconductor into small filaments, compare EP 2 131 407 A1. This approach works well for low temperature superconductor materials, wherein filaments may be easily embedded in a metal matrix.
For high temperature superconductor (HTS) materials with a critical temperature Tc of above 30 K, in particular ceramic superconductor materials, it is common to prepare tape-type superconductors (also called coated conductors), wherein a superconducting layer is deposited onto an elongated non-superconducting substrate (such as a stainless steel tape of several meters length), typically by MOCVD (metal organic chemical vapour deposition), MOD (metal organic deposition) or PLD (pulsed laser deposition). It would be rather difficult to prepare separate stripes of superconducting material on the elongated substrate in these procedures.
EP 0 465 326 B1 reports on an epitaxial YBCO film deposited on a SrTiO3 single crystal substrate, exhibiting a magnetic field induced anisotropy in critical current density. A multilayer structure is proposed to eliminate the magnetic field induced anisotropy.
It is the object of the invention to provide a tape-type superconductor with reduced ac losses.